Conventionally, blow molded containers made of synthetic resins are widely used in applications such as beverages, foods, detergents, cosmetics, and chemicals. Such a container often conceals the content for the purpose, for example, of protecting the content against ultraviolet rays and improving appearance and design quality. Examples of ways of concealing the content from an outside view includes opaquing the container itself with a colored resin, opaquing an outer surface of the container by painting, and applying an overcoat of a shrink film, which is opaque or with opaque printing on a surface thereof, onto the outer surface of the container.
However, concealing the content from the outside view as such poses a problem that the amount of the remaining content may not be identified from the outside, and this leads to inconvenience and anxiety in use. Another problem arising when filling the content again for use is that too much content might be added to cause it to overspill due to invisibility of how much content is filled.
One possible way to overcome the aforementioned problems is to form a window portion, by masking a part of a container which is transparent or semi-transparent and painting the container and by peeling the masking after the painting. In a case of the shrink film, such a window portion may be formed by leaving a portion of the shrink film unprinted and transparent to allow the amount of the remaining content to be identified from the outside.
Furthermore, as described in Patent Literature 1, a blow molded container produced by blow molding an extrusion molded cylindrical parison, that is to say, by direct blow molding, may be relatively easily formed with a transparent window portion in a longitudinal strip shape after the blow molding, by coloring, during the extrusion molding of the parison, a majority of the parison to make the parison opaque while flowing an uncolored transparent resin into a portion of a cylindrical flow path formed in a dice used for the extrusion molding.